(le français suit) These spatial data are the basis for the paper written by J.P. Brandt entitled "The extent of the North American boreal zone" and related map published in the journal Environmental Reviews (17: 101-161, 2009). The circumpolar boreal zone is one of the world's major biogeoclimatic zones, covering much of North America and Eurasia with forests, woodlands, wetlands, and lakes. It regulates climate, acts as a reservoir for biological and genetic diversity, plays a key role in biogeochemical cycles, and provides renewable resources, habitat, and recreational opportunities. Poor agreement exists amongst scientists regarding this zone's delimitation and the areal extent of boreal forests, even though the zone has been well-studied. The paper referred to above reviews the literature on the phytogeography of the zone and makes use of a geographic information system (GIS) and published maps to delineate a current map of the North American boreal zone and the hemiboreal subzone, which is a transitional area lying immediately to the south of the boreal zone that is usually included in the boreal zone by Europeans but excluded by North Americans. On the basis of the map described in the published paper, the boreal zone covers about 627 million ha, or 29% of the North American continent north of Mexico. If the hemiboreal subzone, at 116 million ha, is included, then 34% of the same area is covered. Forests and other wooded land (362 million ha) cover 58% of the North American boreal zone on the basis of current forest inventory data. With forests and other wooded land of the hemiboreal subzone (68 million ha) factored in, this percentage remains basically unchanged. * * * * * * * * * * Ces données géospatiales ont servi de base à la rédaction de l'article de J.P. Brandt intitulé " The extent of the North American boreal zone " ainsi que la carte connexe publiés dans la revue Dossiers environnement (17: 101-161, 2009). La zone boréale circumpolaire constitue une des zones biogéoclimatiques les plus importantes du monde; elle comprend une bonne partie des forêts, des milieux boisés, des terres humides et des lacs de l'Amérique du Nord et de l'Eurasie. Elle régularise le climat, agit comme réservoir de diversité biologique et génétique, joue un rôle dans les cycles biogéochimiques et fournit ressources renouvelables, habitats et lieux récréatifs. Il existe peu de consensus parmi les scientifiques quant à la délimitation de cette zone et sur l'étendue des forêts boréales, bien qu'on ait passablement étudié cette zone. L'article cité en référence présente la documentation sur la phytogéographie de la zone suivie d'une cartographie actuelle de la zone boréale nord-américaine et de la sous-zone hémiboréale générée à l'aide du système d'information géographique (GIS) et de cartes publiées auparavant. Cette cartographie constitue une aire de transition située immédiatement au sud de la zone boréale; les Européens incluent cette région dans la zone boréale, contrairement aux Nord-Américains qui l'excluent. D'après la carte présentée dans l'article publié, la zone boréale couvre 627 millions ha ou 29 % du continent nord-américain, au nord du Mexique. Si on inclut les 116 millions ha de la sous-zone hémiboréale, on atteint une couverture de 34 % de la même région. Les forêts et autres terrains boisés (362 millions ha) couvrent 58 % de la zone boréale nord-américaine, selon les données actuelles des inventaires forestiers. Si on inclut les forêts et autres surfaces boisées de la sous-zone hémiboréale (68 millions ha), ce pourcentage demeure globalement inchangé.
(le français suit) The purpose of the published paper was to develop a revised map of the North American boreal zone and the hemiboreal subzone using consistent criteria and the most current information. * * * * * * * * * * Le but de cet article est de présenter la carte de la zone boréale de l'Amérique du Nord et de la sous-zone hémiboréale qui a été révisée à partir de critères homogènes et de la plus récente information.
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Brandt, J.P., 2009.
The boreal zone is defined as the broad, circumpolar vegetation zone of high northern latitudes covered principally with forests and other wooded land consisting of cold-tolerant trees species primarily within the genera Abies, Larix, Picea, or Pinus but also Populus and Betula; the zone also includes lakes, rivers, and wetlands, and naturally treeless areas such as alpine areas on mountains, heathlands in areas influenced by oceanic climatic conditions, and some grasslands in drier areas. In North America, the boreal zone can be divided into either two or three sub-zones on the basis of the vegetation: the forest-tundra (or subarctic or hemiarctic) at the north; the continuous boreal forest (consisting of closed forests, and open forests or woodlands) generally occupying the mid portion, and the hemiboreal (or sub-boreal) at the south. The tree limit defines the northern boundary of the forest-tundra. The continuous boreal forest subzone is defined by the dominance of closed and open forests consisting of cold-tolerant tree species (see Table 2 of the published paper) primarily within the genera Abies, Larix, Picea, or Pinus but also Populus and Betula. The hemiboreal subzone is defined by the co-occurrence of cold-intolerant tree species, cold-tolerant tree species, and species with intermediate cold-tolerance, with the cold-tolerant species contributing substantially to the forest cover.
The analogue and digital maps used to construct the spatial data varied greatly in scale (e.g., 1:20 000 to 1:8 000 000); the majority of the maps were at a scale of about 1:5 000 000. Thus, display and analysis of the spatial data should be done at an appropriate scale (i.e., between (1:5 000 000 and 1:8 000 000). The user should be aware of three possible sources of error in areal determinations related to mapping: scale, conversion of analogue maps to digital format, and map projection. Generalization occurs in cartography because of five related procedures: selective omission, simplification, combination, exaggeration, and displacement (Keates 1996). Of these five procedures, selective omission and simplification are affected by scale and are most important in the context of the present paper. Selective omission refers to the restriction in display of the feature or phenomenon of the map's theme and is generally a function of scale, geographical density, and relative importance (Keates 1996). For example, the extent of rivers and lakes depicted on a map at 1:50 000 cannot be displayed on a map at 1:1 000 000 without compromising the legibility of the smaller scale map (see Fig. 21 of the published paper). This, in turn, has an impact on the areal statistics of the extent of land and water derived from the two different maps (see Table 5 of the published paper). Additionally, both linear features and outlines presented on a map need to be made less complex than the reality they depict and this is also dependent on scale (Keates 1996). This aspect is apparent when comparing the maps at various scales in Fig. 21 of the published paper. In the studies of Bird (1961), Zoltai (1975), Payette (1983), Timoney (1988), and Archibold and Wilson (1980), aerial photography, aerial surveys, ground surveys, or all three methods were employed to collect the data on which the maps in these publications were based. Presumably the data were captured on relatively large- or medium-scale maps and then reduced to the scale depicted in the publications. During this process, linear features would have been omitted, simplified, or both. Conversion of analogue maps to digital format involves several steps. The analogue map must be scanned. The map projection of the analogue map must then be identified so that a reference layer in the GIS with the same map projection as the analogue map can be opened. The map must be registered by adding control points and transforming the scanned map to the coordinate system of the control points on the reference layer. Next, the scanned map must be georectified. Finally, the spatial information of the scanned map is input into the GIS with heads-up digitizing. One of the key problems in the above steps is that often the map projection of the analogue map is not known and the scanned map must be rubber-sheeted (a GIS term referring to the process of digitally stretching the map) to fit the reference layer. Rubber-sheeting introduces error. A map is a visual representation of part or all of the earth's surface and the success of this representation depends on the map projection chosen to produce the map (Pearson 1990). The earth is an oblate spheroid and both spheres and spheroids have been used to model the earth. Spheres and spheroids have undevelopable surfaces (i.e., they are three-dimensional shapes that cannot be developed onto a plane without distortion (Pearson 1990)). Distortion can occur in area, linear dimensions, angle, or shape, and minimizing distortion of one type leads to increased distortion in the others (Pearson 1990). There are three distinct types of projection: equal-area, conformal, and conventional (Pearson 1990). Equal-area projections preserve the ratio of areas on earth to corresponding areas on a map but they introduce distortion in distance and angle, with the latter suffering the most distortion (Pearson 1990). Equality of areas between the earth and the map (i.e., equal-area) is useful for depicting comparative areal extents of things such as the amount of forest or lakes in different countries, a situation in which distortion in shape and linear scale is acceptable (Fenna 2007). The best equal-area projection for a long narrow strip on the earth (i.e., not exceeding 30-35 degrees of latitude) at about middle latitudes and parallel to a latitude is the Albers equal-area conic (Pearson 1990; Snyder 1993; Kennedy and Kopp 2000). However, Maling (1973) notes that it is difficult to find any projection to depict Canada or Russia in which linear or area distortion is less than 3% or angular deformation is less than 3-5 degrees. The map developed in this paper was projected with Albers equal-area conic projection and standard parallels set at 47.5 degrees N and 54.5 degrees N.
See the logistical consistency report in this metadata or see the published paper: Brandt, J.P. 2009. The extent of the North American boreal zone. Environmental Reviews 17: 101-161.
The maps of North America's boreal zone and its forests were scanned, digitized, and converted to GIS coverages. Maps by Rowe (1972), Marschner (1974), Finley (1976), Ecoregions Working Group (1989), Comer et al. (1995b), Ecological Stratification Working Group (1995), Saucier et al. (1998), Food and Agriculture Organization (2001), Olson et al. (2001), Natural Regions Committee (2006), and British Columbia Ministry of Forests and Range (2006) were available as GIS files. Other maps, listed in the published paper in the regional descriptions, were consulted but were not digitized because (i) these maps had insufficient or inadequate control points to properly geo-reference them for GIS input; (ii) they lacked sufficient detail to warrant digitization; (iii) they were of the same pedigree as an acceptable existing map; (iv) they were superceded by a more recent map; or (v) they were adjacent to but outside the boreal zone. All coverages were converted to the same projection and datum. The GIS was used to view and compare the boundaries of the 32 maps of the boreal zone. Table 3 in the published paper summarizes various aspects of these maps including scale, the methods and materials used to create them, and the criteria used by the authors of the maps to delineate boundaries. To develop a revised map of the North American boreal zone and the hemiboreal subzone using consistent criteria and the most current information, Brandt (2009) used the map of Rowe (1972) for Canada and the map of Viereck and Little (1972) for Alaska as a starting point because these two maps are generally perceived as being accurate for the scale at which they are depicted and they are still widely used in the scientific literature even though they are 37 years old. One of the limitations of both maps that is not widely recognized or acknowledged is that the authors describe only briefly the materials and methods they used to compile their maps (see Table 3 in the published paper). Thus, Brandt (2009) replaced an ecotone boundary depicted on the older maps with a boundary depicted by a more recent study when (i) the more recent study used a criterion the same as or similar to a criterion used in the present paper, and (ii) the more recent study provided a thorough description of materials and methods that should allow repeatable results. In some situations the scale or resolution of data also became a factor; the author of the published paper gave preference to maps at larger scales and data of higher resolution. For boundaries for which a more recent study was not found and for which other data were not readily available, the default boundary was that of either Rowe (1972) or Viereck and Little (1972). The hemiboreal subzone is mapped by neither Rowe (1972) nor Viereck and Little (1972). For this subzone, boundaries were selected from studies compatible with the published paper's definition and meeting the two conditions listed above. Table 4 of the published paper lists the maps that were viewed in the GIS for each boundary and region considered in this paper. There are problematic areas that defy classification on the basis of the definitions and criteria used in this paper. These include treeless coastal areas and islands, mountain areas that result in belts of vegetation, and outliers of distinct vegetation found at different elevations than the surrounding areas. Coastal areas and islands covered with heaths (i.e., treeless), having cool climates moderated by the ocean (i.e., eastern Labrador, parts of Newfoundland, the Aleutians), and lying adjacent to the boreal zone are placed within the boreal zone (Meades 1983; Yurtsev 1994; Talbot et al. 2006). Belts of vegetation in mountain areas have traditionally been classified as montane, subalpine, or alpine. In the published paper, assignment of mountain areas adheres to the following rules to the extent possible given the available data. (i) If the lowest elevations of the valley fall within the boreal zone, then forests at higher elevation are also in the boreal zone; areas above the tree limit are classified as alpine but within the boreal zone. Thus, areal statistics for the boreal zone include treeless, alpine areas but the statistics for these alpine areas are reported separately (like water, see Table 6 of the published paper). (ii) If the lowest elevations of the valley fall within the hemiboreal subzone, then forests at higher elevation consisting of cold-tolerant species are placed in the boreal zone, otherwise (i.e., forests consisting of species of intermediate cold-tolerance) they are classified as hemiboreal. Areas above the tree limit are treated as alpine; these alpine areas are included in the boreal zone when forests immediately below these areas are classified as boreal, or are included in the hemiboreal subzone when the forests immediately below these areas are classified as hemiboreal. (iii) If the lowest elevations of the valley fall within the temperate zone, then forests at higher elevation are classified as being in the hemiboreal subzone if they consist of species of intermediate cold-tolerance and are contiguous with the hemiboreal subzone. If they are not contiguous with forests classified as being in the hemiboreal zone then they are considered montane or subalpine subzones or belts of the temperate zone. Areas above the tree limit are treated as alpine; these alpine areas are included in the hemiboreal subzone when the forests immediately below these areas are classified as hemiboreal. In British Columbia, there are several outlying areas of vegetation usually lying in isolated valleys that are distinct from the surrounding vegetation; these outliers are included in the same zone or subzone as the surrounding vegetation. For example, there are valleys covering a relatively small area with temperate species (i.e., Thuja plicata and Tsuga heterophylla) in northwestern British Columbia east of Skagway, Alaska, that are included in the boreal zone. Other outliers in non-mountainous terrain found at different elevations and with vegetation distinct from surrounding areas are treated similarly; these outliers are also included in the zone or subzone of the surrounding areas. Examples include the Cypress Hills in southern Alberta and Saskatchewan, which is placed in the temperate zone, and the Spruce Woods in Manitoba, which is placed in the hemiboreal subzone.
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